Prediction of the optimal hydrogen storage in high entropy alloys

Abstract

Hydrogen is the most abundant element in nature, characterized by its vast resources, recyclability, and environmentally friendly. Also, it can exist in various forms, such as gas, liquid, or solid, to meet different storage needs. In solid-state storage, the hydrogen storage alloys have received widespread attention due to hydrogen is stored in the form of hydrides. In recent years, high entropy alloys (HEAs), as a new type of novel alloy design concept have attracted a lot of attention in many fields including hydrogen storage due to their unique structures and excellent properties. Moreover, the freedom of element selection leads to various types of HEAs, further enhancing the potential for their application in hydrogen storage. This article focuses on the hydrogen storage performance of HEAs and provides a comprehensive overview of the hydrogen storage mechanism, thermodynamics, and kinetics. Additionally, we summarize and compare the hydrogen storage capacities of previously published HEAs and introduce two empirical parameters, valence electron concentration (VEC) and atomic size difference (δ), and their relationship with hydrogen storage capacity. By applying the K-means clustering algorithm, we conclude that the optimal hydrogen storage capacity of HEAs occurs when 4 <VEC < 6 and 5.3 % <δ < 7.5 %. This finding offers valuable guidance for the future design of efficient hydrogen storage HEAs.